A Simple Two-Column Layout

Step 2 - the two divs are now aligned vertically. The navigation div (with its right border in red so you can see where it is) has been absolutely positioned so it is removed from the flow of the document.

As an absolutely positioned element, its default position is in the top left corner of its containing element, the body element.

This allows the content div to take its place as the first element in the document flow.